1. Field of the Invention
The present invention relates to a rotary driving apparatus suitable for use, for example, in a fluid control valve device.
2. Description of the Prior Art
There has heretofore been known a rotary valve device provided with an electromagnetic driving apparatus applying a drive force to the valve body for opening or closing control. During the de-energized condition, a spring acts to keep the valve body in a first position. The supply of an electric current creates an electromagnetic force moving the valve body against the spring to a second position. When the electric current is stopped, the spring acts to return the valve body from the second position to the first position. With such an apparatus, it has been possible to increase the speed of return of the valve body from the second position to the first position by increasing the spring force. The increased spring force, however, means more of a force the electromagnetic force has to overcome when moving the valve body from the first position to the second position, causing decreased speed of valve body movement in that operation. Thus, the prior art has suffered from the drawback that it cannot achieve a quick change of the valve position in both directions.
As a prior art for obtaining better response, there has heretofore been known the use of two coils to eliminate the return spring, as described in Japanese Laid-Open Patent Application No. 55-33041. The use of two coils in the valve housing, however, results in a new disadvantage of increased dimensions of the device.